Melt blown and spunbond webs typically comprise insoluble and nondegradable polymer fibers such as water insoluble polyethylene, polypropylene, polyester and polyamide. Such webs are used in the manufacture of a variety of disposable products such as disposable diapers, feminine napkins, surgical gowns, laundry bags, bed pads, and the like. Such articles are designed to absorb and contain bodily fluids and/or provide a physical barrier to such fluids. Water soluble and biodegradable nonwoven webs may provide some solutions to environmental concerns regarding the disposal of such items.
Heat fusible webs are used for a variety of uses. In the textile industry, heat fusible webs are used to hold pieces of fabric, such as a patch pocket, in place prior to being sewn. These heat fusible webs are also used to create hems on pants or for a variety of ornamental craft appliques. Webs currently available for such uses are typically low viscosity at application temperature and insoluble in water. Upon activation with heat these materials often soak into the fabric workpiece causing the fabric to become stiff. Often the melted web soaks in to the extent that it fails to form the intended bond and reapplication is necessary.
A water soluble nonwoven comprising polyvinyl alcohol (PVOH) is taught in Dever et al., JP 59041260. Modifying the rate of water solubility of a PVOH based melt blown material using two different chemical treatments is described in the Development and Evaluation of Water Soluble Melt Blown Nonwovens, Dever, Benson, and Pair, INDA JNR, Vol. 5, No. 2, published 1993.
PVOH as a base polymer for the formation of a water soluble web suffers from several disadvantages. Due to its high melt point and poor thermal stability, it is very difficult to thermally process. An extruder, rather than merely a melt tank, is required to process the PVOH into a web. Additionally, once the web is formed, it has poor heat seal properties such that it would need to be heat sealed at temperatures that adversely affect the integrity of the substrate.
Water soluble polyamides prepared from an aliphatic dicarboxylic acid, a modifying acid, and an aliphatic diamine are reported by Fagerberg et al., U.S. Pat. No. 3,882,090. The polyamides are useful as textile sizing agents, coatings, and adhesives. Column 4, lines 28-33 states, "The various methods of preparing polyamides are well known in the art as well as a number of polymers which contain ether linkages in the polymer chain. These however, are basically fiber forming polyamides and therefore not contemplated by the present invention."
Speranza et al., U.S. Pat. Nos. 5,053,484; 5,086,162; 5,324,812 and 5,118,785 are directed to certain polyamides having good water absorbency for use as fibers. Collectively, the polyamides taught therein either exhibit a high melt point, much like the PVOH, requiring an extruder for processing into a nonwoven web, or in the case of those polyamides having lower melt points, are disadvantageous in that the polyamides, once formed into a fiber or nonwoven web, tend to block. At column 1, lines 21-16 the 5,324,812 patent discusses that several nylon manufacturers incorporate polyoxyalkyleneamines into their products to modify the final properties. The polyether backbone of these components improves the comfort feel, wickability and dyeability of textile grades. However, no such compositions have been used to form a water soluble nonwoven web.
The Applicants have found that certain water soluble polyamides exhibit improved melting characteristics for manufacturing fibers as well as spunbond and melt blown nonwoven webs. Further, the resulting fibers and webs are water soluble, humidity resistant and nonblocking, meaning the web can be rolled upon itself and subsequently unwound without adjacent layers adhering to each other.